cifs: don't update i_size in cifs_do_truncate without a cached handle

Overview

In the Linux kernel, the following vulnerability has been resolved:

cifs: don't update i_size in cifs_do_truncate without a cached handle

If find_writable_file() returns null, cifs_file_flush will return 0 without issuing set_file_size, and the outer 'if (!rc)' block will set i_size to 0 before telling the server to truncate. If the cifs_open() then fails, the inode will have size 0, while the server file is unchanged.

Move the netfs_resize_file() and cifs_setsize() into the 'if (cfile)', so they only run after a successful set_file_size.

In the no-handle else branch, evict stale pages with truncate_inode_pages before the O_TRUNC open to dispose of old cache pages, and let the open response set the i_size.

Affected

• Linux >= 110fee6b9bb58a5c50047fc2594d415f741b591e < 04d020b3d0b58a1b7e116900e4095b96a7f4e11a
• Linux >= 110fee6b9bb58a5c50047fc2594d415f741b591e < 88a51743cd8094b76fd910f53f718747c7729cc8
• Linux >= 110fee6b9bb58a5c50047fc2594d415f741b591e < fe39cd9d48f2346605f3746e0cc19e89d5f373eb
• Linux 6.18

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.